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    Home > Coatings News > Paints and Coatings Market > Pain point analysis and solutions for ultra-high-gloss water-based 2KPU applications in wood paint.

    Pain point analysis and solutions for ultra-high-gloss water-based 2KPU applications in wood paint.

    • Last Update: 2020-10-07
    • Source: Internet
    • Author: User
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    After more than 20 years of wild growth in China, water-based industrial coatings have ushered in the dawn of a great leap forward in market share with the collection and implementation of the VOC consumption tax. In 2017, the oil-to-water of container coatings took the lead, extending to the field of construction machinery in 2018, while the water-based nature of the rail transit sector was also on the agenda, coupled with the accumulation of the furniture industry and low-end anti-corrosion field over the years, industrial paint water-based has become a star-stinging trend.
    water-based two-part polyurethane (2KPU) technology is considered by many to be the ultimate solution for wood coatings because of its physical properties comparable to solvent-based 2KPU and superior to water-based single-group self-crossed acrylic . Especially in office furniture, hotel furniture, kitchen furniture and other high-end applications, water-based 2KPU is often the first choice for paint. However, so far, water-based 2KPU has only been successfully used in half-gloss/matte systems, with a small market share, while the application of ultra-high-gloss systems has not yet achieved large-scale mass production.
    Ultra-high-gloss water-based 2KPU pain point analysis
    01, high raw material costs
    from the water-based 2KPU ultra-high-gloss varnish cost dismantling, familiar with the formula engineers are well aware that the raw material costs mainly come from water-based curing agents. Although the dosage is only about 15%, but according to the unit price of 80 yuan / kg conservative estimate, curing agent spent 12 yuan / kg, equivalent to a single component of acrylic market quotation.
    , hydroxy-containing ingredients (generally dominated by hydroxypropyl acrylic emulsions) also account for about 30% of raw material costs. In order to achieve ultra-high-gloss plump effect, engineers have to use relatively expensive high hydroxy emulsion, especially in the use of secondary dispersion as the main resin, water-based 2KPU coating raw material cost can reach 2 times or more of a single-part acrylic coating.
    02, poor construction adaptability
    In order to unilaterally pursue high-gloss, high plumpness, formula engineers often in accordance with inertial thinking to adopt secondary dispersion matching. However, most of the secondary dispersants contain solvents, and considering its relatively slow dry properties, coupled with the curing agent reaction time is relatively long, hardness will be very slow to build up, so the early stacking performance is poor, can not keep up with the pipeline production beat, seriously affecting production efficiency, easy to be applied end-of-the-line disease.
    03, high rework rate
    ultra-high-gloss system of water-based 2KPU, in order to achieve the ultimate perfect appearance, the actual production often needs to accurately control the application of the process (including coating volume, waiting time and temperature and humidity conditions). This indirectly increases labor or equipment costs. However, the production conditions of the furniture industry is indeed relatively rough, technicians hand-operated level is also uneven, in the absence of the necessary equipment modification and standard operating procedures, often appear thick film foaming and other paint film defects (Figure 1-2), and ultra-high light is more likely to make people aware of defects, repair rate naturally increased. The resulting commercial compensation and labor costs, so that paint manufacturers do not pay off, so that formula engineers dare not easily the ultra-high-gloss system industrialization.
    Figure 1 - The appearance of thick film foaming
    Figure 2 - Magnifier picture of thick film foaming (50x magnification)
    A careful summary of the above pain points reveals that this is more or less related to the characteristics of secondary dispersions (as shown in Table 1). But looking at the primary dispersion, it can make up for the deficiency of the secondary dispersion to some extent, if we can do a better job of gloss and plumpness, it may also provide us with solutions.Table
    1 - Comparison of Primary dispersions and secondary dispersions
    Experimental Part
    JONCryl® OH8770 ap, developed and produced by BASF in China, is based on the above ideas and is specifically designed for ultra-high-gloss water-based 2KPU formulations. We compared Joncryl® OH 8770 ap with a secondary dispersion commonly used on the market, choosing raw materials that are compatible with both sides and making them into high-gloss varnishes, based on the following test methods to compare the performance of high-gloss varnishes.
    experimental raw materials
    . Joncryl® OH 8770 ap, Hydropalat® WE 3221, FoamStar® SI 2280, Rheovis ® PU 1191, Dispex Ultra PX 4 575: BASF New Materials Co., Ltd.; Target Products: Other Foreign Companies; BDG, DMEA, Propylene Glycol, Ethanol: National Pharmaceutical Group Chemical Reagents Co., Ltd.; Tioxide® R 706: Chemours, Inc. All raw materials are industrial grade.
    01, test equipment
    portable gloss instrument, swing bar hardness tester, wire rod -100 microns: BYK Company;
    02, paint preparation
    water-based varnish preparation: A part according to table 2 emulsion stirring state at 600rpm, in turn according to the formula slowly added to each raw material, all A ingredients added, and then evenly and fully stirred 15 minutes.
    water-based white paint preparation: according to table 3 formula will be divided into 15 microns of grinding, white water-based white pulp. When making white paint, the table 2 varnish and table 3 white paste by the quality ratio of 5:1 mixed evenly, to obtain white water-based paint.
    Table 2 - Joncryl® OH 8770 ap and Test Formula for The Underlying Product
    Table 3 - White Water-based Slurry Formula
    03, Sample Paint Film Preparation
    Paint Film: Using Black and white paper jam, glass board or PET film, reference GB /T9271-1988 preparation paint film test board, using 100 micron wire rod for coating film, paint film dry film thickness of 25 to 30 microns. After 7 days of room temperature maintenance, it is used to test the luster, transparency, hardness and stain resistance of paint film.
    04, Performance
    . Paint film gloss: according to GB/T9754-2007;
    . Paint film plumpness: according to the coating rate of 120g/m2 spray construction 4 varnishes (considered as 2 primers plus 2 finishes), visual comparison assessment;
    . paint film transparency: preparation of paint film on PET film, drying through the mist imager to measure the fog shadow value;
    , emulsion transparency: visual comparison assessment;
    paint film pencil hardness: measured by GB/T6379-2006;
    . scratch-resistant preservation rate: scraping 100 micron wet film on TheLeneta paper, drying at room temperature for 4 hours, drying at 50 degrees C for 16 hours, measuring the original Gloss (60 degrees), load 5 0 0g weight, weight under the 3M standard sandpaper (model 3M2 8 1QWETORDRY, diameter 3.5cm), friction 20 times back and forth, measure the gloss after scratching (60 degrees), calculate the preservation rate. The preservation rate is the luster/original gloss after scratching, and the chemical resistance
    the
    paint film: as measured by ISO-MAT-0066-R2.
    results and discussion
    01, paint film gloss and plumpness
    From the test results in Figure 3, it can be seen that Joncryl® OH 8770 ap gloss performance is very good, especially at a 20 degree angle gloss can be maintained at more than 85GU, significantly better than the market for the standard products. Figure 4 paint film appearance comparison can be learned: Although Joncryl® OH 8770 ap paint film three-dimensional sense is not so strong, but overall plumpness can meet the requirements, fully in line with the design expectations of the primary dispersion. The main reason is to benefit from the type and proportion optimization of the monosome used in synthetic emulsion, but due to the fast-drying properties of the emulsion itself, the flattening time of the paint film is shortened, and gloss and plumpness will be sacrificed.
    Figure 3 - Glossy contrast of ultra-high-gloss varnishes
    Figure 4 - Contrast of the appearance of the paint film of ultra-high-gloss varnishes
    the transparency of the paint film and emulsion
    the transmission and fog-shadow values measured by the mist screen instrument reveal that Joncryl® OH8770 ap and the dry film permeability of the underlying product are very close, while the translucation of the emulsion itself is slightly different (Figure 5). The appearance of the emulsion can be improved by controlling the particle size of hydroxypropyl emulsion, and the average particle size can be translucent at about 80 to 100 microns. In addition to the influence of emulsion particle size, the wet membrane permeability of the coating is also affected by drying conditions, film-forming conditions, and the compatible of the parts, the reasons are relatively complex.
    Figure 5 - Comparison of hydroxypropyl emulsion permeability
    03, Physical Resistance
    by comparing the physical properties of two 2KPU formulations at different NCO/OH ratios in Table 4, although there is no particularly significant difference in pencil hardness However, Joncryl® OH 8770 ap's early swing bar hardness and scratch-resistant preservation rate are higher than the standard product, especially under NCO/OH 1.2 conditions, the difference will be more obvious. Using the same formula in practice, the client also feedbacks that Joncryl® OH 8770 ap is indeed better stack-resistant than the benchmark product. This is mainly due to the increased glass temperature of hydroxypropyl emulsion, which helps the emulsion itself to become faster and drier, effectively and quickly establish the hardness of the paint film, and improve the stack resistance of the paint film.
    Table 4 - Joncryl® OH 8770 ap and the physical performance of the subject product at different NCO/OH ratios
    04, Chemical Resistance
    Testing the chemical resistance of the dry film found that Joncryl® OH 8770 ap and the subject product in high-gloss varnishes are not very different, because the main resin in the formulation is large, ensuring chemical resistance. In the stain resistance test of the paint, we chose yellow mustard as the test medium, and the test found that the traces of Joncryl® OH 8770 ap were significantly lighter (Figure 6). This may be because, in addition to using hydroxyl and isocyanate curing agents, Joncryl® OH 8770 ap has introduced self-intersecting groups, resulting in improved performance.
    Figure 6 - Comparison of yellow-resistant mustard in color paint
    From the above application test results, Joncryl® OH 8770 ap performs well except for a slight gap in plumpness (as shown in Figure 7). In practical applications, water-based 2KPU formulations can be used for performance adjustment with Joncryl® OH 8770 ap mixing slow-dry secondary dispersions, just like traditional solvent-based 2KPU coatings, through multiple resins with multiple curing agents, to achieve complementary performance advantages. Note, however, that the compatibness of the blended resin must be screened.
    Figure 7 - Joncryl® OH 8770 ap and the main performance comparison of the standard products
    conclusion
    the hydration of industrial coatings has been a major trend, with the "blue sky defense war" of the east wind, water-based industrial coatings will certainly be developed by a large amount of time, and solvent-based wood coatings in China market share will gradually be replaced by UV coatings and water-based 2KPU coatings. The Joncryl® OH 8770 ap described in this article, with fast drying, fast hardness development, stack-resistant characteristics, is an ultra-high-gloss high-abundance 2KPU coating breakthrough products, while its curing agent demand is low, can effectively reduce the risk of dark bubbles, more suitable for use on the production line, but also has excellent chemical resistance, formula engineers may wish to try.
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